Drill attachment



March W26 1,577,895

J. A. CONARD DRILL ATTACHMENT Filed July :50, 1921 m -n E 1;

Patented Mar. 23, 1926.

rice.

JAMES A. CONARD, or new YORK, n. Y;

' DRILL ATTACHMENT.

Application filed July 30,

T0 aZZ whom it may concern: 1

Be it known that I, JAMns A. Cont nen a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and, useful Improvements in Drill Attachments, of which the following is a specification.

This invention relates to a protective casing for drills, and more particularly for line drills which are of small diameter in comparison with their length, and hence especially liable to breakage.

When the cutting edges of fine drills meet an obstruction which they cannot overcome, the drills, because of their comparatively great length, are easily broken due to bending or to torsional strain, or a combination of both, which exceeds the limit of elasticity of the drill. It is one feature of this invention to provide a protective casing for the drill which shall eliminate the possibility of breakage due to any of the causes above mentioned.

It will be understood that in the ordinary. drilling process the edges are constantly meeting and overcoming obstructions, and in i this manner bore their way into a piece of work. In overcoming these ordinary obstructions there is a slight bending or twist ing of the drill which is highly desirable, for if the drill were absolutely unyielding the edges would soon become worn. It is another feature of this invention, therefore, that while preventing such bending or twisting of the drill when it meets an extraordinary obstruction as will break the drill, it nevertheless allows for sufficient yielding of the drill when meeting ordinary obstructions in the cutting operation to prevent wearing of the cutting edges.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

Figure 1 is a front elevation of-the invention applied to a drill;

Figure 2 is a view similar to Figure 1, the protective casing being shown vertically sectioned;

Figure 3 is a section taken on the line 3-3 of Figure 2; and

Figure 4 is a section taken on the line t-t of Figure 2. I

Referring to the drawings, there is illustrated a drill 10 of small diameter in comparison with its length, and having a shank 1921. Serial No. 488,726.

portion at one end for insertion in a 'rotatingchuck and provided at its other end with a cutting edge 11.

The invention comprises a protective casing in the form of a sheath or tube '12 provided with a central bore of two diameters,

the upper bore 13 being of a. diameter to allow the shank of the drill to fit snugly therein; and the lower bore 14: being of greater diameter and concentrically disposed with respect to'bore 13, and hence concentrically disposed with respect to the drill when housed within bore 13. The amount by which the diameter of bore 14 exceeds the diameter of bore 13 is determined by the amount of bending or lateral play Which occurs when the drill overcomes the ordinary obstructions in the cutting process, and is usually slight, as shown in dotted lines in Figure 2. It will be apparent that the snug fit of the shank of drill 10 in bore 13 in efiect reduced the length of drill 13, and hence reduces the amount of bending to which it is liable. Should the cutting edge, however, meet an extraordinary obstruction which would tend to bend the drill excessively, the latterwill strike against the wall of bore 14 practically tangentially and without injury to the edge, and there is thus eliminated the danger ofbreaking by excessive bending.

The tendency of the drill to break by twisting or torsional strain is overcome by shortening the effective length of drill. This is accomplished by clamping the drill, at a point intermediate its length, to the casing, and for this purpose a set-screw 15 having a suitable finger-piece 16 is threaded through a boss 17 of a collar 18 slid on and fastened to the casing in any suitable manner, said set-screw passing through an opening 19 in the casing to clamp the shank of the drill to the wall of bore 13. The effective length of drill, i. e., the length which is subject to torsional strain, is thus reduced by the distance from the upper end of the drill (see Fig. 2) to the shoulder formed by the meeting of the bores 13 and 14. The set-screw may not be applied to bore 14, for it would then press the drill to one side and destroy the concentric positioning of the drill within the bore 14 which permits equal lateral play on all sides. The collar 18 and boss 17 provide the support for the screw 15 which could not be supplied by the comparatively thin wall of the casing. By

loosening set-screw 15) the amount of cutting edge 11 which projects beyond the end of the casing may be regulated at Will.

From the above description it Will .be .apparent that While breaking of the drill clue to bending or twisting is eliminated by the protective casing, a slight degree of lateral play or bending is permitted within bore 14;, and the portion of the drill below the setscrew in Figure 2 is subject to slight twist, such slight bending and twisting facilitating the Work of ordinary drilling Without danger of breaking the drill; It will be understood also that the upper poirtion of the casing enclosing the shank of the drill is inserted and clamped in the rotating chuck Variations may be resorted to Within the scope of the annexed claim.

Ayguarcl for preventing the breaking of drills by excessive bending, such drills each having a shank portion at one end and a cutting portion at the other end, said guard comprising a protective casing having at. one end a tubular bore into which the shank portion of a drill fits snugly, and having also a bore slightly larger than the drill forming a continuation of said first bore and concentrically disposed With respect to the said first bore to permit slight lateral displacement of the cutting portion of the drill equally in directions Within the langer bore, excessive displacement being prevented by the contact of the drill with the Wall oil? said larger bore and means for rigidly holding the shank of the drill in the smaller bore.

In testimony whereof I :aflix my signature.

JAMES A. comment 

